A series of secret ceasefire deals have been agreed with Taliban commanders to ensure that voting can go ahead in Afghanistan's volatile south during next week's presidential elections.

Under the deals, brokered by Ahmed Wali Karzai – the controversial brother and campaign manager of the president, Hamid Karzai – individual Taliban commanders will agree to pull back on election day and allow the Afghan army and police to secure the polling centres.

A Nato spokesman confirmed that a number of deals between the Afghan government and insurgents were in the pipeline, saying: "We support any initiative that enhances security and enables the people of Afghanistan to vote."

The US embassy has given its blessing to the plan, which was discussed last week at a joint meeting of the country's national security chiefs.

Many of the key negotiations with local Taliban commanders in the south are being handled by Wali Karzai, who is also the powerful head of Kandahar's provincial council. He is running his brother's re-election campaign in the southern Pashtun belt.

The Guardian was told by Wali Karzai that truces in some of the country's most violent provinces, including Helmand and Kandahar, would be announced in the next few days with individual commanders. The deal would allow for more polling stations to open; officials had said that as many as 700 of the country's 7,000 voting centres would stay closed.

Wali Karzai said that commanders were split on whether or not to follow the orders of Mullah Omar, the Taliban leader, who wanted the election disrupted. "It will all depend on the group and who they are connected with. Some Taliban leaders will look the other way, but others will say no, stop them, this is helping the Jew and the Christian in this war."

The prospect of the south being unable to vote has worried the Afghan president, who needs the votes of his fellow Pashtuns, the largest ethnic group in Afghanistan, to ensure victory without having to go to a second-round run-off. It also alarmed western powers anxious that the strife-torn region might be further destabilised if the election were won by a candidate who did not enjoy support in the Pashtun belt.

Wali Karzai said many local Taliban commanders shared those fears despite the stance of Omar. "I just had a meeting with a very, very, influential Taliban commander," he said. "I told him, look, the election will happen despite these four provinces participating or not. Whether we take part or not, the election will happen because Afghanistan is 32 provinces – they are not going to wait for what Kandahar is going to do."

Asked whether the Taliban were concerned at the prospect of low-voter turnout in the south letting a non-Pashtun win the election, he said: "Absolutely, they are saying this, they understand this. How can it be that in the 'war on terror' the frontline is the Pashtun? How can the Pashtun become an opposition in this war? What will happen if there is a Pashtun civilian casuality? Right now we have a president who will take the matter up."

Wali Karzai is a controversial figure. The older half-brother of the president, he enjoys huge power in Kandahar and is alleged to be involved in drug trafficking, a claim he vociferously denies.

he rebutted a report in the German news magazine Stern that British forces had seized tonnes of opium on his land last month. He claimed this was a political attack aimed at hurting the president before the elections.

But speaking at his home in Kandahar , he exuded confidence about the prospects for his brother's re-election, saying rivals, including the former foreign minister Abdullah Abdullah, did not have extensive support.

He said: "We have absolutely the complete support of 90% or 95% in the south. How to bring people to the polling stations will be our major concern next week. My challenge in organising this thing is security, it's not Abdullah Abdullah or Ashraf Ghani."

Taliban ceasefires allowing voters to turn out in the Pashtun heartland will be a big boost to the re-election plans. The official line from Taliban spokesmen based in Pakistan is that Afghans should not participate in the election. There have also been threats to disrupt election day by blocking roads leading to the polling centre and intimidating voters.

Taliban commanders are reported to have threatened to kill anyone they find with a finger marked with indelible ink – a stain meant to prevent people from voting more than once.

However, a western expert in Kandahar, with extensive knowledge of the security situation in the south, said that Taliban threats to disrupt the election had been half-hearted. "I don't see a well articulated mass of oppositions to the electoral process – we have seen incidents in recent weeks, but it is not systematic."

Wali Karzai warned, however, that some groups would be implacable, including that of Mullah Dadullah, a senior Taliban commander killed in 2007. "I will only really know which groups have kept their promise after the election," he said.

Many analysts believe one of the reasons the elections in 2004 went relatively smoothly was because of international pressure on Pakistan to rein in militants operating in Afghanistan with links to the Pakistani intelligence service.

"I hope that happens again – last time it was like someone just pressed a button to stop these people coming in from over the border," Wali Karzai said.

He also revealed that a number of tribal militias would be mobilised in the south to help guarantee security at election centres – a move that has been denounced by democracy activists who fear it will make electoral fraud easier.

It is thought that armed men controlled by local militia leaders could intimidate many people into voting for their preferred candidate, or even commit outright election fraud such as ballot box stuffing.

Jandad Spinghar, the chief executive of the Free and Fair Elections Foundation in Afghanistan, said militias were a threat to the election.

"They can interfere with the process because they have local power. Their presence will also stop our observers from reporting on the election freely and fairly."